The present invention generally relates to the separation of solid particles, such as soot, from a fluid, such as oil, by use of a centrifuge. More specifically, but not exclusively, one embodiment of the present invention relates to a centrifuge that includes two separate fluid paths in which one of the fluid paths travels through a particulate collection zone of the centrifuge and the other path bypasses the particulate collection zone to directly drive the centrifuge through jet nozzles. In a related embodiment, the collection chamber receives a single batch of fluid for processing without any flow-through of fluid during the processing of this single batch.
Diesel engines are designed with relatively sophisticated air and fuel filters (cleaners) in an effort to keep dirt and debris out of the engine. Even with these air and fuel cleaners, dirt and debris, including engine-generated wear debris will find a way into the lubricating oil of the engine. The result is wear on critical engine components and if this condition is left unsolved or not remedied, engine failure. For this reason, many engines are designed with full flow oil filters that continually clean the oil as it circulates between the lubricant sump and engine parts.
There are a number of design constraints and considerations for such full flow filters and typically these constraints mean that such filters can only remove those dirt particles that are in the range of 10 microns or larger. While removal of particles of this size may prevent a catastrophic failure, harmful wear will still be caused by smaller particles of dirt that get into and remain in the oil. In order to try to address the concern over small particles, designers have gone to bypass filtering systems which filter a predefined percentage of the total oil flow. The combination of a full flow filter in conjunction with a bypass filter reduces engine wear to an acceptable level, but not to the desired level. Since bypass filters may be able to trap particles less than approximately 10 microns, the combination of a full flow filter and bypass filter offers substantial improvement over the use of only a full flow filter.
In high performance soot centrifuge (HPSC) designs, such as the one disclosed in U.S. Pat. No. 6,019,717 that was issued on Feb. 1, 2000 to Herman, which is incorporated by reference in its entirety, the inventors of the present invention have found that the collection rate of super-fine particulates, such as soot, increases by decreasing the flow rate passing through the rotor of the centrifuge. Traditional centrifuge theory predicts that reducing the flow rate in the rotor by half will result in a doubling of the single-pass collection efficiency of the centrifuge. Although the collection efficiency improves, since the flow rate is cut in half, the collection rate of particulates should remain unchanged. Graph 30, which is show in FIG. 1, graphically illustrates this predicted effect for super-fine particles, such as soot. As shown, graph 30 includes a flow rate axis 32 and a collection rate axis 33. Prediction line 35 in graph 30 illustrates the prediction that flow rate through the centrifuge has no effect on the collection rate. However, the inventors of the present invention have discovered that this theory does not appear to hold up in super-fine particulate regime where collection efficiencies are typically well under 0.5% on a single pass basis. As shown with actual line 36, the collection rate of the super-fine particles increases as the flow rate is decreased. It is theorized that the collection rate is improved at the lower flow rate though reduced re-entrainment of particulates in the fluid. The reduced flow rate diminishes fluid eddies and flow passing in close proximity to the collected particles (sludge) in the sludge collection zone of the centrifuge, which in turn reduces the amount of re-entrainment of the collected particles. The HPSC design allows for the freedom to reduce the rotor “through flow” rate without penalizing rotor speed. In the HPSC design, the fluid flow driving upon an external Pelton turbine is independent from the rotor flow rate so that the flow rates can be independently adjusted.
Unfortunately, in the lower cost and widely used hero-turbine centrifuge designs, (such as the ones disclosed in U.S. Pat. No. 5,795,477 that was issued on Aug. 18, 1998 to Herman et al. which is incorporated by reference in its entirety) simply reducing the rotor through flow to take advantage of this effect, does not work. In the hero-type centrifuges, a single flow path is used for both separation of particulates from the fluid and driving the centrifuge. Reducing the flow rate in the rotor reduces rotor speed because the rotation driving power is proportional to the rotor flow rate. One type of solution, such as disclosed in U.S. Pat. Nos. 3,784,092 and 5,906,733, is to provide two separate fluid sources, one for driving the centrifuge and the other for separation. However, using the two separate fluid sources in these designs increases the complexity and expense of the centrifuge. Furthermore, retrofitting such types of centrifuges to pre-existing systems is costly because additional piping needs to be installed.
A further embodiment of the present invention configures the centrifuge and rotor such that the incoming fluid flow follows a flow pattern or path that first fills the rotor collection chamber with a single batch or charge of fluid (oil) that continues to be cleaned until shut down and then drains. Once the collection chamber is filled, the incoming flow is routed to the jet nozzle openings for self-driven rotor rotation, without any continuous flow-through of fluid through the collection chamber or collection zone.